Certain surgical procedures such as oncology surgery and major revision surgery require the resection of the proximal humerus where critical soft tissues (i.e. rotator cuff) attach to the bone. It is typical in these surgeries to bring previously detached tendons to the implant and suture them to the prosthesis. Soft tissue attachment is critical to maintaining movement about the joint and preserving joint stability. It has been difficult to obtain secure attachment of these soft tissues to prostheses for multiple reasons.
First, in natural attachment to bone, there is a transition region of soft tissue to bone (i.e. muscle-tendon-bone) that changes gradually from flexible to rigid. In the reattachment of soft tissue to prosthesis, this transition region is often lost and failure often occurs due to the abrupt change from soft tissue to very rigid metal implants.
Second, in certain procedures resection of surrounding soft tissues along with bony resections are required (i.e. resection to obtain adequate surgical margins during the removal of bone cancer such as osteosarcoma or where bone loss is significant from multiple revision surgeries). This soft tissue resection often leaves the remaining soft tissues too short to reach their original attachment sites, even if adequate methods of attachment directly to metal were available.
Currently, several methods are used to create a functional bridge between soft tissue and prostheses. These methods have exhibited limited success. Where there exists enough length for the soft tissue to reach the prosthesis, the soft tissue is often sutured directly to the prosthesis. Advances have been made in the material and surface treatment of the attachment sites (i.e., the use of porous or foam metals) to improve and promote the in-growth of soft tissue after surgery. However, the relative stiffness of these attachment sites compared to the soft tissue being attached continues to be a limiting factor in the end strength of the tissue/implant interface.
In some joints, when soft tissue length is not adequate to reach the natural attachment site on the prosthesis, graft is sometimes used to create a bridge. Autograft (via transplant or flap) can help to provide additional functional length of the soft tissue, but does not address the stiffness issue. Also, function of the graft host site is also reduced. Furthermore, in the proximal humerus, there are not significant neighboring structures to create substantial tissue flaps for coverage and augmentation of tissue length. Allograft is also an option, however again stiffness is not addressed and known issues of rejection and/or lack of integration with the graft tissue exist. Synthetic materials such as aorta-graft have been used to create a sleeve or bridge between the prosthesis and bone. This can address the stiffness issue at the attachment soft tissue attachment site, however the lack of direct integration of the synthetic material with the prosthesis means that long term loads must be borne by sutures or other attachment mechanisms. As a result, failure of the interface may merely move from the muscle/graft interface to the graft/prosthesis interface.
Typical soft tissue attachment to a humeral prosthesis are shown in U.S. Pat. Nos. 3,803,641, 5,330,531 and 6,398,812 as well as U.S. Patent Application Publication No. 2007/0078516.
In all of the above cases, the preparation and attachment of all of these grafts requires significant time and effort during the surgical setting, which exposes the patient to additional operating room (OR) time in what may be an already lengthy surgical procedure.